Optical semiconductor bare chip, printed wiring board, lighting unit and lighting device

ABSTRACT

A wiring board used for mounting an LED bare chip capable of firmly bonding the LED bare chip and improving yield. In a printed wiring board  2 , a distance D between wiring patterns  81  and  85  disposed so as to oppose each other is the smallest at a position nearest to a center point (G) of an LED chip  14  disposed at a designed location, and increases with an increasing distance from the point G. In addition, pattern edges  83  and  87  of the wiring patterns  81  and  85  recede in the direction of widening the distance D as a distance from the center point G increases with respect to electrode edges  148  and  149  of the LED chip  14.

TECHNICAL FIELD

The present invention relates to an optical semiconductor bare chip suchas an LED, a printed wiring board used for mounting an opticalsemiconductor bare chip thereon, a lighting unit, and a lightingapparatus.

BACKGROUND ART

In the field of lighting apparatus, a study has been conducted for usingLED bare chips for a lighting apparatus by densely mounting manyone-side-electrode type LED bare chips on a printed wiring board(hereinafter simply called “a wiring board”) by a flip chip method usingultrasonic bonding. In the lighting apparatus, each LED chip has severalhundred μm square in size and has p-electrodes and n-electrodes on onesurface.

FIG. 18A is an enlarged plan view showing an LED chip 710 flip-chipmounted on a wiring pattern 701 for a p-electrode and a wiring pattern702 for an n-electrode, both attached to a wiring board 700. In FIG.18A, to make a clear distinction between the LED chip 710 and the wiringpatterns 701 and 702, the LED chip 710 is drawn with thick lines and thep-electrode 711 and the n-electrode 712, which are disposed on thereverse side (the under surface) of the LED chip 710, are drawn asviewed through the LED chip 710.

As shown in FIG. 18A, the p-electrode 711 and the n-electrode 712 on theone surface of the LED chip 710 are disposed so as to oppose each otherand have a distance d therebetween (e.g. d is approximately 20 μm, wherethe LED 710 is 300 μm square).

Meanwhile, the wiring patterns 701 and 702 are disposed so as to opposeeach other and have the distance d therebetween in accordance with theshapes of the corresponding p-electrode 711 and n-electrode 712. Here,the p-electrode 711 and the n-electrode 712 on the LED-chip 710 areelectrically connected to the wiring pattern 701 and the wiring pattern702 respectively so as to have surface contact, using the ultrasonicbonding.

Such a lighting apparatus is generally supplied with large amount ofelectricity to gain high optical output. Therefore, large amount of heatis liberated, and this might cause cracks at the junction of the LEDchip 710 and the wiring board 700 due to the difference of thermalexpansions. To avoid this problem, conventional arts increase the powerlevel of the ultrasonic bonding, thereby increase the bonding strength.

However, if the bonding strength is increased by increasing the powerlevel of the ultrasonic bonding, the LED chip 710 might be rotated acertain angle, as shown in FIG. 18B, from the position that the LED chip710 should take when it is mounted (“normal mounting position”, theposition illustrated in FIG. 18A), and the p-electrode 711 and then-electrode 712 might short out (in areas indicated by a sign a). Thereason why this happens is the following. A flip chip bonder is used formounting the LED chip 710. The flip chip bonder bonds the LED chip 710,which is attracted to the tip of a collet, to the wiring board 700 byapplying ultrasonic vibration while placing and pressing the LED chip710 onto the designed mounting location. If the power level isincreased, the LED chip 710 wobbles by rotating a little around thecollet as the rotation axis, and the LED chip 710 might be mounted afterit is rotated from its normal mounting position. If the short circuit iscaused, the LED does not function as a matter of course, and processingsuch as remounting will be required. This considerably reduces yields.

Such a problem can be caused not only in the case of mounting the LEDchips, but also in the case of mounting optical semiconductors such assemiconductor lasers by the above-described method.

DISCLOSURE OF THE INVENTION

In view of the above problems, the present invention aims to provide anoptical semiconductor bare chip, a printed wiring board for mounting theoptical semiconductor bare chip thereon, a lighting unit, and a lightingapparatus, which are capable of firmly bonding the optical semiconductorbare chip, such as an LED chip, with use of a conventional flip-chipbonder, and improving yields.

The above object is fulfilled by a printed wiring board having first andsecond wiring patterns that are formed on a mounting surface thereof soas to oppose each other across an insulating region, an opticalsemiconductor bare chip being flip-chip mounted on the mounting surfaceand having, on one surface thereof, first and second electrodes that aredisposed so as to oppose each other, and the first and second wiringpatterns respectively corresponding in position and shape to the firstand second electrodes, wherein in a plan view of the insulating regiondivided into a first region that includes a point nearest to a centerpoint of the optical semiconductor bare chip that takes a normalmounting position, and second and third regions that sandwich the firstregion, (i) an outer edge portion of the first wiring pattern whichadjoins the second region, and an outer edge portion of the secondwiring pattern which adjoins the third region, and/or (ii) an outer edgeportion of the first wiring pattern which adjoins the third region, andan outer edge portion of the second wiring pattern which adjoins thesecond region, are formed so as to recede inwardly as a distance fromthe center point increases with respect to outer edges of the first andsecond electrodes of the optical semiconductor bare chip that takes thenormal mounting position.

Accordingly, even if the power level of the ultra sonic bonding at thetime of the flip-chip mounting is increased and the opticalsemiconductor bare chip is mounted after it is rotated from its normalmounting position, the stated structure makes it possible to prevent thefirst electrode (e.g. the p-electrode) and the second electrode (e.g.the n-electrode) from causing a short circuit. Also, it becomes possibleto improve yield, and prevent cracks occurring at the junction. This isrealized by forming the receding parts at positions which are assumed tobe in contact with the first and second electrodes when the opticalsemiconductor is mounted after it is rotated, and forming the outeredges of the first and second wiring patterns in the receding parts soas to recede inwardly not to be in contact with the outer edges of thefirst and second electrodes of the rotated optical semiconductor barechip.

Here, in a case where a distance between the first and second electrodesmeasured at any point is substantially constant, the width of the firstregion is substantially constant and substantially equal to the distancebetween the first and the second electrodes.

In the case where a distance between the first and second electrodesmeasured at any point is substantially constant, the stated structureimproves the yield and prevents cracks occurring at the junction.

The first and second wiring patterns are formed on a surface of aninsulating plate that is a composite substrate including an inorganicfiller and a resin composite. This makes it possible to manufacture theprinted wiring board at low cost, and makes processing such asmultilayering easy.

A lighting unit according to the present invention is a lighting unit inwhich an optical semiconductor bare chip is flip-chip mounted on aprinted wiring board thereof, wherein the above-described printed wiringboard is used as the printed wiring board used for mounting thereon theoptical semiconductor bare chip.

A lighting apparatus according to the present invention is a lightingapparatus comprising the above-described lighting unit as the lightsource.

An optical semiconductor bare chip according to the present invention isan optical semiconductor bare chip having first and second electrodesthat are disposed on one surface thereof so as to oppose each otheracross an insulating region, the semiconductor bare chip being flip-chipmounted on a mounting surface of a printed wiring board having first andsecond wiring patterns that are formed on the mounting surface so as tooppose each other, the first and second wiring patterns respectivelycorresponding in position and shape to the first and second electrodes,wherein in a plan view of the insulating region divided into a firstregion that includes a point nearest to a center point of the opticalsemiconductor bare chip, and second and third regions that sandwich thefirst region, (i) an outer edge portion of the first electrode whichadjoins the second region and an outer edge portion of the secondelectrodes which adjoins the third region, and/or (ii) an outer edgeportion of the first electrode which adjoins the third region and anouter edge portion of the second electrode which adjoins the secondregion, are formed so as to recede inwardly as a distance from thecenter point increases with respect to outer edges of the first andsecond wiring patterns that respectively correspond to the first andsecond electrodes of the optical semiconductor bare chip that takes anormal mounting position.

Accordingly, even if the power level of the ultra sonic bonding at thetime of the flip-chip mounting is increased and the opticalsemiconductor bare chip is mounted after it is rotated from its normalmounting position, the stated structure makes it possible to prevent thefirst electrode (e.g. the p-electrode) and the second electrode (e.g.the n-electrode) from causing a short circuit. Also, it becomes possibleto improve yield, and prevent cracks occurring at the junction. This isrealized by forming the receding parts at positions which are assumed tobe in contact with the first and second electrodes when the opticalsemiconductor is mounted after it is rotated, and forming the outeredges of the first and second electrodes in the receding parts so as torecede inwardly not to be in contact with the outer edges of the firstand second wiring patterns of the rotated optical semiconductor barechip.

Here, in a case where a distance between the first and second wiringpatterns measured at any point is substantially constant, the width ofthe first region is substantially constant and substantially equal tothe distance between the first and the second wiring patterns.

In the case where the distance between the first and second wiringpatterns measured at any point is substantially constant, the statedstructure improves the yield and prevents cracks occurring at thejunction.

A lighting unit according to the present invention is a lighting unit inwhich an optical semiconductor bare chip is flip-chip mounted on aprinted wiring board, wherein the above described optical semiconductorbare chip is used as the optical semiconductor bare chip that is to bemounted on the printed wiring board.

A lighting apparatus according to the present invention is a lightingapparatus comprising the above-described lighting unit as the lightsource.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a lighting unit 1 according to the firstembodiment;

FIG. 2 shows details of a LED chip 14 and its vicinities;

FIG. 3 is a cross-sectional view of an LED chip 14 and a printed wiringboard 2, which are cut along a line B-B in FIG. 2 and viewed in thedirection represented by arrows in FIG. 2;

FIG. 4 is a plan view of wiring patterns 81 and 85, on which an LED chip14 is not mounted yet;

FIG. 5 is a plan view of a surface of an LED chip 14, on whichelectrodes are disposed;

FIG. 6 is a plan view showing an example case where an LED chip 14 ismounted after it is rotated in the direction shown by an arrow;

FIG. 7 is a plan view of a reverse surface of an LED chip 90 accordingto the second embodiment, on which electrodes are disposed;

FIG. 8 is a plan view showing configurations of wiring patterns 96 and98 via which an LED chip 90 is mounted on a wiring board 2;

FIG. 9 is a plan view showing an LED chip 90 which is mounted exactly ona designed mounting location;

FIG. 10A shows example pattern configurations of a wiring pattern 102used for a p-electrode and a wiring pattern 103 used for an n-electrodeaccording to a modification of the present invention, and FIG. 10B showsother example pattern configurations;

FIG. 11A shows example configurations of a p-electrode and ann-electrode on an LED chip 110 according to a modification of thepresent invention, and FIG. 11B shows example configurations of wiringpatterns 115 and 116 in the case where the LED chip 110 is used;

FIG. 12 shows another configuration of a wiring pattern according to amodification of the present invention;

FIG. 13A shows example configurations of a p-electrode 131 and ann-electrode 132 on another LED chip 130 according to a modification ofthe present invention, and FIG. 13B shows example configurations ofwiring patterns 133 and 134 in the case where the LED chip 130 is used;

FIG. 14 is a plan view showing example configurations of a p-electrode151 and an n-electrode 152 on an LED chip 150 according to amodification;

FIG. 15A shows a modification of a configuration of a wiring pattern inthe case where an LED chip 150 is rotated clockwise at the time of themounting, and FIG. 15B shows the same in the case where the LED chip 150is rotated anti-clockwise at the time of the mounting;

FIG. 16 shows example shapes of a p-electrode and an n-electrode of anLED chip of a modification;

FIG. 17 is a perspective view showing a structure of a lightingapparatus 200 using a lighting unit 1;

FIG. 18A is an enlarged plan view showing a conventional LED chip 710flip-chip mounted on a wiring pattern 701 for a p-electrode and a wiringpattern 702 for a n-electrode at a normal mounting position; and

FIG. 18B shows a LED chip 710 mounted after it is rotated a certaindegree from its normal mounting position.

BEST MODE FOR CARRYING OUT THE INVENTION

The following describes embodiments of the present invention, withreference to the attached figures.

The First Embodiment

FIG. 1 is a plan view of a lighting unit 1 according to the firstembodiment. The lighting unit 1 includes sixty-four LED chips 11 to 74mounted on a wiring board 2 in an orderly manner so as to form a matrixhaving eight rows and eight columns. (The first row, the second row . .. and the eighth row are arranged from top to bottom, and the firstcolumn, the second column . . . and the eighth column are arranged fromleft to right.) Here, each of the LED chips 11 to 74 measures 300 (μm)in length and width in plan view.

The wiring board 2 has a structure in which a plurality of layersincluding substrates 3 and 4 (two layers in this embodiment) includingwiring patterns 8 and 7 made of metal formed on the surfaces ofinsulating plates 5 and 6 (see FIG. 3) made of a thermosetting resinincluding an inorganic filler. In FIG. 1, only the top substrate 3 isvisible. In this embodiment, the insulating plates 5 and 6 use aluminacomposite substrates that include alumina as an inorganic filler andepoxy as a thermosetting resin. The wiring patterns 7 and 8 use gold(Au). The wiring patterns 7 and 8 are formed mainly for connecting, ineach column, the LED chips in odd-number rows and the LED chips ineven-number rows in series.

FIG. 2 shows the details of an area A in FIG. 1, which includes an LEDchip 14 at the intersection of the first row and the fourth column andits vicinity. FIG. 3 is a cross-sectional view of an LED chip 14 and aprinted wiring board 2, which are cut along a line B-B in FIG. 2 andviewed in the direction represented by arrows in FIG. 2. FIG. 4 is aplan view of a mounting surface of the wiring board 2, on which the LEDchip 14 is not mounted yet. FIG. 5 is a plan view of a surface of theLED chip 14, on which electrodes are disposed. FIG. 2 shows an examplecase where the LED chip 14 taking the normal mounting position isdisposed exactly on a designed mounting location, without beingdisplaced (or rotated). To make clear distinction between the LED chip14 and wiring patterns 81 and 85, the LED chip 14 is drawn with thicklines, and an anode electrode (p-electrode) 145 and a cathode electrode(n-electrode) 146, which are disposed on the reverse side (the undersurface) of the LED chip 14, are drawn as viewed through the LED chip14.

As shown in each figure, the LED chip 14 has a structure in which anAlInGaN-based N-type layer 142, an active layer 143 and an AlInGaN-basedP-type layer 144 are laminated on a sapphire substrate 141 which isinsulative and transparent, and the power is fed to the LED chip 14 viathe p-electrode 145 disposed on the P-type layer and the n-electrode 146disposed on the N-type layer.

Meanwhile, positions of one end portion 82 of a first wiring pattern 81and one end portion 86 of a second wiring pattern 85, both included inthe wiring pattern 8, correspond to the positions of the p-electrode 145and the n-electrode 146 respectively. The shapes of the end portions arerespectively similar to the shapes of the electrodes as well.

The LED chip 14 has a structure in which the p-electrode 145 and then-electrode 146 are disposed so as to oppose each other on one surfaceof the LED-chip 14. The LED chip 14 is to be mounted by the flip chipmethod, and as mounted, the p-electrode 145 of the LED chip 14 iselectrically connected to the one end portion 82 of the wiring pattern81 and the n-electrode 146 of the LED chip 14 is electrically connectedto the one end portion 86 of the wiring pattern 85. Obviously, the otherend portion of the wiring pattern 81 is to be connected to then-electrode of an LED chip 16 (FIG. 1), and the other end portion of thewiring pattern 85 is to be connected to the p-electrode of an LED chip12.

As described in Background Art, the flip chip bonder (not illustrated)is used for mounting the LED chip 14. The flip chip bonder is anapparatus that bonds the LED chip 14 onto the wiring board 2 bycontrolling the motion of a stage carrying the wiring board 2 to adjustthe designed mounting location on the wiring board 2 to the position ofthe collet holding the LED chip 14 carried from other place and standingstill, lowering the collet, and applying ultrasonic vibration for apredetermined period while pressing the LED chip 14 onto the wiringboard 2.

More specifically, two recognition marks (not illustrated) are preformedon the insulating plate 5 so that the center point of the designedmounting location (the point H shown in FIG. 4) is located between themarks. The flip chip bonder recognizes the positions of the recognitionmarks by an image recognition device, and calculates the position of thecenter point of the designed mounting location (the point H) from theresult of the recognition. Meanwhile, the flip chip bonder recognizesthe LED chip 14 held by the collet, and calculates the position on theX-Y plane of the center point of the LED chip 14 (the position on theX-Y plane of the intersection of lines that bisect the LED chip 14lengthwise and breadthwise respectively: the point G shown in FIG. 5)from the shape of the LED chip 14. Then, the flip chip bonder calculatesthe amount of the difference between the center point of the designedmounting location and the center point of the LED chip 14, and adjuststhe position of the stage by moving the stage by the calculated amount.The flip chip bonder also calculates amount of the difference betweenthe position that the LED chip 14 should take (normal mounting position)and the position that the LED chip held by the collet takes (i.e. howmuch the LED chip is rotated from its normal mounting position). Ifthere is such a difference, the flip chip bonder rotates the collet (onits axis) to correct the difference. After that, the flip chip bonderlowers the collet (the LED chip 14 is to be placed on the designedmounting location on the wiring board 2), and performs the ultrasonicbonding.

The LED chip according to the present invention is for use with alighting unit. Therefore, the power level of the ultrasonic vibration(more specifically the amplitude level) is several times larger comparedto the case where the LED chip is for use with a display device and soon. The power level is usually approximately 200 (mW) when the LED chipis for use with a display device and so on, but in this case the powerlevel is increased to approximately 1500 (mW) to mount the LED chip.More specifically, pressure at approximately 150 (g), and the ultrasonicvibration having a frequency of approximately 60 (kHz) and amplitudewidth of several μm is applied to the LED chip for approximately 0.3seconds. Due to this ultrasonic vibration, the LED chip might be mountedafter rotated by several degrees (approximately 2° here) from its normalmounting position. However, in case the LED chip is mounted in such arotated position, the shapes of the wiring patterns 81 and 85 in thepresent invention are designed to prevent the p-electrode 145 and then-electrode 146 from causing a short circuit, as described later.

The p-electrode 145 and the n-electrode 146 are disposed so as to opposeeach other across an insulating region 150. In plan view, the width d ofthe insulating region 150 (i.e. region between the p-electrode 145 andthe n-electrode 146, hereinafter called the “electrode opposed region”)measured at any point in the region is constant (approximately 20 μmhere), just as a conventional LED chip. To realize high light-extractionefficiency, the width d is as narrow as possible in the manufacturingprocess.

Meanwhile, the wiring patterns 81 and 85 on the wiring board 2 aredisposed so as to oppose each other across an insulating region 89. Inthe insulating region 89 (i.e. the region between the wiring patterns 81and 85, hereinafter called the “pattern-opposed region”), the patterndistance D is shortest when measured in the first region (the regionindicated by an arrow C, hereinafter called “the region C”) including apoint C′ that is nearest to the point H (substantially nearest to thepoint G), where D=D1 (approximately 20 μm). In the second region (theregion indicated by an arrow E, hereinafter called “the region E”) andthe third region (indicated by an arrow E′, hereinafter called “theregion E′”), which are located on both sides of the region C, thepattern distance D becomes longer as the distance from the point Hincreases, and the largest value of the distance D is “D2”(approximately 40 μm).

FIG. 2, as a plan view of the LED chip 14 taking its normal mountingposition, shows that in the regions (the regions E and E′) in which thepattern distance D becomes longer as a distance from the point Hincreases, pattern edges (outer edges) 811 and 812 of the wiring pattern81 and pattern edges (outer edges) 851 and 852 of the wiring pattern 85,which adjoin the regions E and E′, draw apart from electrode edges(outer edges) 148 and 149 so that the pattern distance D becomes longeras a distance from the point H increases (In other words, with respectto the electrode edges 148 and 149 of the respective p-electrode 145 andn-electrode 146 included in the LED chip 14 taking its normal mountingposition, the pattern edges 811, 812, 851 and 852 recede (move back)inwardly as the distance from the point H (G) increases).

Such receding parts are made for preventing the p-electrode 145 and then-electrode 146 from causing a short circuit in the case where the LEDchip 14 is mounted after it is rotated a several degrees from its normalmounting position.

In other words, as described in Background Art, the LED chip wobblesaround the collet. The LED chip wobbles, on the wiring board 2, aroundthe center point of the collet or its vicinity as the center point ofthe rotation in clockwise or anticlockwise direction. In thepattern-opposed region 89, the amount of the wobble (moving distance)becomes larger in the regions E and E′ that are far from the point G (H)than in the region C that is near to the point G (H). It is difficult tojudge in which of the clockwise direction and the anticlockwisedirection the LED chips is to be rotated from its normal mountingposition (and to take a rotated position) before it is bonded onto thewiring board 2. (It is highly likely that the direction varies for eachLED, depending on the surface condition of the wiring board 2, presenceor absence of bumps, and the shapes of the bumps.

Therefore, the short circuit is prevented regardless of the rotativedirection by shaping the pattern edges 811 and 812 of the wiring pattern81 and the pattern edges 851 and 852 of the wiring pattern 85 so thatthe distance D becomes longer as the distance from the center point (thepoint G) of the LED chip 14 increases. In other words, the pattern edges811 and 812 of the wiring pattern 81 and the pattern edges 851 and 852of the wiring pattern 85 do not lap over the reach of the wobble of theelectrode edges 148 and 149 of the p-electrode 145 and the n-electrode146 for preventing the short circuit.

The region C is near to the center point of the LED chip 14, and it isto be hardly affected by the rotation. Therefore, in the region C, thedistance between the patterns is made as short as possible so as tomatch the distance (“d”) between the areas on the LED chip 14corresponding to the region C. This maintains sufficient bonding areasbetween the p-electrode 145 and the wiring pattern 81 and between then-electrode 146 and the wiring pattern 85, thereby increases the bondingstrength.

FIG. 6 is a plan view showing an example case where an LED chip 14 ismounted after it is rotated in the direction shown by an arrow (theanticlockwise direction). The wiring patterns 81 and 85 of theembodiment of the present invention (illustrated in full line) and thoseof the conventional art (illustrated in dashed line) are both shown inFIG. 6. Note that the degree of the rotation is illustrated withexaggeration, and the actual rotation angle θ is less than 3° (0°<θ<3°).

As shown in FIG. 6, in the present invention, the pattern distance inthe pattern-opposed region becomes longer as the distance from thecenter point of the LED chip 14 increases, and therefore the p-electrode145 and the n-electrode 146 do not short out. To the contrary, in theconventional art, the pattern distance in the pattern-opposed region isconstant at anywhere in the region, and therefore the p-electrode 145and the n-electrode 146 short out at two points. FIG. 6 shows the casewhere the LED chip 14 is rotated anticlockwise from its normal mountingposition. However, also in the case where the LED chip 14 is rotated thesame degrees clockwise to from the normal mounting position, thep-electrode 145 and the n-electrode 146 do not short out in the presentinvention. This is because the pattern edges 811, 812, 851 and 852recede inwardly as the distance from the center point (point G) of theLED chip 14 increases, so that the pattern edges 811, 812, 851 and 852do not lap over the reach of the wobble of the electrode edges 148 and149 of the p-electrode 145 and the n-electrode 146. If the LED chip 14is mounted after rotated from its normal mounting position, it is not aproblem for use of the LED chip 14 as a light source, because it doesnot affect the light distribution characteristic and so on.

Therefore, if the LED chip 14 is mounted after rotated from its normalmounting position because of the increased power level of the ultrasonicbonding at the time of the flip chip mounting, the p-electrode 145 andthe n-electrode 146 do not cause a short circuit, and this significantlyimproves the yield ratio at manufacturing. Further, sufficient bondingarea is maintained by forming the region C in the pattern-opposed region89 so as to have the pattern distance that is almost equal to thedistance between the electrodes on the corresponding LED chip (insteadof just making the distance between patterns longer), and thereforesufficient bonding strength is maintained. This prevents cracksoccurring at the junction between the LED chip 14 and the wiring board 2due to the difference of thermal expansions between the LED chip 14 andthe wiring board 2. As a result, the present invention can achieveeffects of bonding the LED chip firmly to the wiring board and improvingthe yield ratio.

In the case where the wiring board 2 is made of resin, the power levelof the ultrasonic bonding is required to be high because such a wiringboard is softer than a silicon substrate and so on. Therefore, if thisis the case, it is more likely that the LED chip 14 is mounted in therotated position. However, the above-described structure improves theyield ratio in such a case. Therefore, the present invention isparticularly effective in cases in which a substrate made of resin isused.

Furthermore, in the case of forming the wiring pattern by etching, itbecomes easy to fill the pattern-opposed region with etching solutioncompared with the conventional art, because the width of thepattern-opposed region in the present invention becomes narrower as thedistance from the center point becomes shorter, whereas width of thepattern-opposed region in the conventional art is almost constant atanywhere. Therefore, the present invention can achieve effects ofimproving the yield ratio in the etching process as well.

The shape of the LED chip 14 and the shapes of the wiring patterns 81and 85 on which the LED chip 14 is to be mounted are described above.However, other LED chips 11, 12, 13, and 15 to 74 have the same shape asthe LED chip 14, and the pattern shapes of the areas on which LED chipsare to be mounted are the same as the above-described wiring patterns 81and 85 as well. Each LED chip is to be mounted by the flip chip bonderone by one, in the same manner as the LED chip 14.

Here, the amounts of the inward recessions of the pattern edges 811,812, 851 and 852 from the electrode edges 148 and the 149 of the LEDchip 14 taking the normal mounting position are properly set accordingto the rotation angle of the LED chip rotated by the ultrasonic bonding.The rotation angle is previously calculated by experiments.

Specifically, in the regions E and E′ shown in FIG. 2, an angle α formedby the pattern edge and the electrode edge that correspond to each other(e.g. 812 and 148, 852 and 149) satisfies 0<α. The angle α is largerthan the maximum angle of the wobble of the electrode edge, which isformed by the rotation of the LED chip at the time of the mounting. Morespecifically, considering that the rotation angle θ (FIG. 6) of the LEDchip at the time of the mounting is less than 3° and the angle α is anapproximation of the above-described angle θ, it is preferable that theangle α is, for instance, 3° or more than 3° (It is preferable that theupper limit is an angle that does not obstruct the bonding).

Furthermore, Z<D1<D2 (Formula 1) and D1+L*tan θ+Z<D2 (Formula 2) may besatisfied, where, in the pattern-opposed region 89, “D1” is the patterndistance of the area that is nearest to the center point of the LEDchip, “D2” is the pattern distance of the area that is farthest from thecenter point of the LED chip, “0” is the maximum rotation angle at thetime of the mounting (the rotation angle at the time when the LED chipis rotated the maximum degrees from the normal mounting position), “Z”is the difference between the designed mounting location and the actualmounting location in the case where the LED chip is mounted on thewiring board 2 after its position is adjusted by the collet in themanufacturing process (This difference is caused depending on theperformance of the collet, such as the pitch of the movement.) (Thedifference “Z” is, more specifically, a distance between theabove-described points G and H measured in the direction that isparallel to the width direction of the above-described distance D2.),and “L” is the side length of the LED chip (i.e. the length of a side ofthe LED chip mounted on the wiring board 2, which is almost orthogonalto the width direction of the above-described distance “D2”.) In thecase where the difference Z is negligible, D1+L*tan θ<D2 may besatisfied.

As described above, it is known by experiments that the rotation angle θof the LED chip is substantially less than 3°. Therefore, also in thiscase, the distance D2 can be calculated by setting 3° or more than 3°(an angle that does not obstruct the bonding) to “θ” in tan θ.

The Second Embodiment

The shapes of the wiring patterns for the p-electrodes and then-electrodes on the wiring board are designed to prevent the shortcircuit in the above-described first embodiment. The second embodimentis about the designs of the shapes of the electrodes on the LED chip. Inthe following description, the same signs are used for representing thematerials and the things that are the same as those in the firstembodiment.

FIG. 7 is a plan view of a reverse surface of an LED chip 90 accordingto the second embodiment, on which electrodes are disposed, and FIG. 8is a plan view showing configurations of wiring patterns 96 and 98 viawhich the LED chip 90 is mounted on the wiring board 2. FIG. 9 is a planview showing the LED chip 90 which is mounted exactly on the designedmounting location. In FIG. 9, to make clear distinction between the LEDchip 90 and wiring patterns 96 and 98, the LED chip 90 is drawn withthick lines, and a p-electrode 91 and an n-electrode 93 are drawn asviewed through the LED chip 90.

As shown in each figure, the width of the pattern-opposed region 100(the insulating region) between the wiring patterns 96 and 98 is d(approximately 20 μm) without variation.

Meanwhile, in the electrode-opposed region 95 (the insulating region) ofthe LED chip 90, the electrode distance is shortest when measured in thefirst region (the region indicated by an arrow J, hereinafter called“the region J”) including a point J′ that is nearest to the center pointof the LED chip 90 (the point G), where D is “D1” (approximately 20 μm).In the second region (the region indicated by an arrow K, hereinaftercalled “the region K”) and the third region (indicated by an arrow K′,hereinafter called “the region K′”), which are located on both sides ofthe region J, the electrode distance becomes longer as the distance fromthe point G increases, and the largest value of the electrode distance Dis “D2” (approximately 40 μm).

In the regions K and K′, electrode edges (outer edges) 911 and 912 ofthe p-electrode 91 and electrode edges (outer edges) 931 and 932 of then-electrode 93, which adjoin the regions K and K′ respectively, drawapart from a pattern edge (outer edge) 97 of the wiring pattern 96 and apattern edge 99 of the wiring pattern 98 so that the electrode distancebecomes longer as a distance from the point G increases. In other words,with respect to the pattern edges 97 and 99 of the respective wiringpatterns 96 and 98 corresponding to the p-electrode 91 and then-electrode 93 of the LED chip 90 taking the normal mounting position,the electrode edges 911, 912, 931 and 932 recede (move back) inwardly asa distance from the point H increases, so that the electrode edges 911,912, 931 and 932 do not contact with the pattern edge 97 of the wiringpattern 96 and the pattern edge 99 of the wiring pattern 98.

Just as in the first embodiment, such receding parts are made forpreventing the p-electrode and the n-electrode from causing a shortcircuit in the case where the LED chip 90 is mounted after it is rotateda several degrees from its normal mounting position. This significantlyimproves the yield ratio at manufacturing, and prevents cracks occurringat the junction.

Note that each of the other sixty-three LED chips has the same shape asthat of the LED chip 90, and the shape of the wiring pattern for eachLED chip is the same as that of the wiring patterns 96 and 98.

Just as in the first embodiment, the amounts of the inward recessions ofthe electrode edges are properly set according to the rotation angle ofthe LED chip rotated by the ultrasonic bonding. The rotation angle ispreviously calculated by experiments. The positional relation betweenthe electrode edges and the pattern edges in the regions K and K′ issubstantially the same as that in the first embodiment. Therefore, asFIG. 9 shows, at the time when the LED chip takes the normal mountingposition, an angle β (the counterpart of the above-described angle α)formed by the pattern edge and the electrode edge that correspond toeach other (e.g. 911 and 97, 931 and 99) can be calculated in the samemanner as in the first embodiment. Further, it is possible to set D2 andso on so as to satisfy the above-described formulas 1 and 2, as in thefirst embodiment.

Modifications

The present invention is described above based on the embodiments.However, the present invention is not limited to the embodiments. Thefollowings are possible modifications.

(1) The shapes of the wiring patterns in the first embodiment are notlimited to the above-described shapes. For instance, the wiring patternsmay have shapes shown in FIG. 10. In FIG. 1A, a wiring pattern 102 forthe p-electrode in the pattern-opposed region 101 has almost the sameshape as the above-described wiring pattern 81, but a pattern edge 104of the wiring pattern 103 for the n-electrode differs from theabove-described wiring pattern 85 in that the pattern edge 104 is bendedat a point 105.

In FIG. 10B, a wiring pattern 106 for the n-electrode has almost thesame shape as the above-described wiring pattern 85, but a pattern edge108 of the wiring pattern 107 for the p-electrode differs from theabove-described wiring pattern 81 in that the pattern edge 108 is bendedat a point 109.

(2) The first embodiment describes, as FIG. 5 shows, an example of theshapes of the wiring patterns in the case where the LED chip having thestructure in which the n-electrode is disposed on a corner of asubstantially square-shaped sapphire substrate. However, in the casewhere a LED chip 110 having the structure shown in FIG. 11A is used, theshape of the wiring patterns may be those shown in FIG. 11B.

In FIG. 11A, a sign 111 indicates a p-electrode on the LED chip 110, asign 112 indicates an n-electrode on the LED chip 110, and the distancebetween the p-electrode 111 and the n-electrode 112 in aelectrode-opposed region 113 is constant, that is approximately 20 (μm)here. In FIG. 11B, a sign “115” indicates a wiring pattern for thep-electrode, and a sign “117” indicates a wiring pattern for then-electrode. In this figure, the conventional wiring patterns areillustrated in dashed line for comparison. A point G is the center pointof the LED chip 110, and a point H is the center point of the designedmounting location on which the LED chip 110 is to be mounted.

As FIG. 11B shows, the distance between the wiring patterns 115 and 117in a pattern-opposed region 119 is the shortest (e.g. approximately 20μm) in a region M including a point M′ that is nearest to the point H.The distance increases in the regions N and N′, which are on both endsof the region M, as the distance from the point H increases, and thedistance is the longest (e.g. approximately 40 μm) when it is measuredat the farthest point from the point H. In the regions N and N′, thepattern edges 116 and 118 draw apart from the electrode edges(illustrated in dashed line) of the p-electrode 111 and the n-electrode112 on the LED chip 110 taking its normal mounting position so that thedistance becomes longer as a distance from the point H increases. (Thepattern edges 116 and 118 inwardly recede so that the electrode edges donot lap over the reach of the wobble of the electrode edges, which iscaused by the rotation at the time of the flip chip mounting.)

Therefore, even if the LED chip 110 is mounted after it is rotated fromits normal mounting position at the time of the flip chip mounting, thep-electrode and the n-electrode do not cause a short circuit, and thissignificantly improves the yield ratio at manufacturing and preventscracks occurring at the junction part.

FIG. 12 shows a modification of the wiring patterns in FIG. 11B. A partof the pattern edge 116 is bended at a part 121, and a part 122 of thepattern edge 118 is formed so as to be parallel to the opposed part ofthe pattern edge.

(3) As FIG. 13A shows, the LED chip 130 may have a structure in whichthe distance D in the electrode-opposed region between a p-electrode 131and an n-electrode 132 becomes longer as a distance from the point Gincreases. In this case, the distance d in the pattern-opposed areabetween a wiring pattern 133 for the p-electrode and a wiring pattern134 for the n-electrode may be constant as shown in FIG. 13B.

Note that in the above-described pattern edge of the wiring pattern inthe pattern-opposed region, the bended part has an angular shape.However, the part may have a curved shape. Also, the pattern edge is notlimited to a straight line. The pattern edge may be a curved line or maybe in a staircase pattern.

In other words, the shape of each pattern edge (outer edge) is notlimited to any particular shape as long as the pattern edge includes areceding part that recedes inwardly as the distance from the centerpoint of the LED chip increases with respect to the electrode edge ofthe LED chip so that the pattern edges do not lap over the reach of thewobble of the electrode edges caused by the rotation at the time of theflip chip mounting. Therefore, if an LED chip has an electrode-opposedregion in which the distance is not constant, the wiring patterncorresponding to the LED chip should be formed so that the pattern edgesdo not lap over the reach of the wobble of the electrode edges, which iscaused by the rotation at the time of the flip chip mounting. The sameis true on the electrodes edges in the electrode-opposed region.

(4) As an example arrangement of the electrode of the LED chip, thestructure shown in FIG. 14 may be used. In an LED chip 150, ap-electrode 151 is in a shape of a cross, and four n-electrodes 152 aredisposed in the unoccupied space. In each electrode-opposed region 153between the p-electrode 151 and the n-electrode 152, the shortestelectrode distance is in the first region (the region between points Fand F′, which are the bending points of electrode edge (the partcorresponding to a line segment that has a constant minute width andconnects the point F with the point F′)) including the point F that isnearest to the point G. In the second region (indicated by an arrow W)and the third region (indicated by an arrow W′), which are located onboth sides of the first region, the electrode distance becomes longer asthe distance from the center point (the point G) increases, and theelectrode edge 154 of the p-electrode 151 and the electrode edge 155 ofthe n-electrode 152 draw apart (recede inwardly) from the pattern edgesof the wiring patterns for the p-electrode and the n-electrode of theLED chip 150 taking its normal mounting position (i.e. the wiringpattern of which the width of the pattern-opposed region is constant andsubstantially the same as the width of the above-described first region.Not illustrated.) so that the electrode distance D becomes longer as adistance from the point G increases. Accordingly, the p-electrode andthe n-electrode do not cause a short circuit at the time of the flipchip mounting.

The LED chip 150 in this example, the electrode-opposed region 153 isL-shaped in the plan view, which is bent at the point F nearest to thecenter point G. Therefore, the line segment that has a constant minutewidth and connects the point F and the point F′ is assumed as a regionand called the first region. However, in the case where the wiringpattern, not the electrode, has such a shape, the bending point (thecounterpart of the above-described line-segment part) may be assumed asthe first region and the regions on both ends of the first region may beassumed as the second and the third regions respectively.

(5) In the abode-described first embodiment, the pattern edges 811 and812 of the pattern edge 81 and the pattern edges 851 and 852 of thepattern edge 85 are formed so as to recede inwardly, as the distancefrom the center point of the LED chip increases, with respect to theelectrode edges 148 and 149 of the p-electrode 145 and the n-electrode146, because it is difficult to judge in which direction the LED chipsis to be rotated from its normal mounting position before it is mounted.

However, there are cases where the rotative direction can be judged fromthe shape of the electrodes and the wiring patterns at the surface ofthe junction, the shapes of bumps and so on. In such cases, it ispossible to form the pattern edges so that the receding part is formedonly on the side corresponding to the rotative direction.

FIG. 15A is a plan view of the wiring pattern, showing an example shapeof the wiring pattern for the case where the rotative direction of theLED chip has judged to be clockwise.

In this modification shown in FIG. 15A, in the pattern-opposed region89, the pattern edge 851 of the wiring pattern 85 adjoining the region Eand the pattern edge 812 of the wiring pattern 81 adjoining the regionE′ are formed so as to recede inwardly (draw apart), as the distancefrom the center point H of the LED chip increases, with respect to theelectrode edges 148 and 149 (illustrated in broken line) of thep-electrode 145 and the n-electrode 146 of the optical semiconductorbare chip taking the normal mounting position. The pattern edge 811 ofthe wiring pattern 81 adjoining the region E and the pattern edge 852 ofthe wiring pattern 85 adjoining the region E′ do not recede inwardly(not draw apart), which means that they are at the conventionalpositions as FIG. 6 shows.

In this way, by forming the pattern edges so as to recede inwardly andnot to lap over the reach of the wobble of the electrode edges, which iscaused by the rotation at the time of the flip chip mounting, it becomespossible to prevent the p-electrode and the n-electrode from causing ashort circuit in the case where the LED chip is mounted after it isrotated clockwise several degrees from its normal mounting position.

FIG. 15B is a plan view of the wiring pattern, showing an example shapeof the wiring pattern for the case where the rotative direction of theLED chip has judged to be anticlockwise.

In FIG. 15B, on the contrary to FIG. 15A, in the pattern-opposed region89, the pattern edge 811 of the wiring pattern 81 adjoining the region Eand the pattern edge 852 of the wiring pattern 85 adjoining the regionE′ are formed so as to recede inwardly (draw apart), as the distancefrom the center point H of the LED chip increases, with respect to theelectrode edges 148 and 149 (illustrated in broken line) of thep-electrode 145 and the n-electrode 146 of the optical semiconductorbare chip taking the normal mounting position. The pattern edge 851 ofthe wiring pattern 85 adjoining the region E and the pattern edge 812 ofthe wiring pattern 81 adjoining the region E′ do not recede inwardly(not draw apart), which means that they are at the conventionalpositions as FIG. 6 shows.

In this way, by forming the pattern edges so as to recede inwardly andnot to lap over the reach of the wobble of the electrode edges, which iscaused by the rotation at the time of the flip chip mounting, it becomespossible to prevent the p-electrode and the n-electrode from causing ashort circuit in the case where the LED chip is mounted after it isrotated anticlockwise several degrees from its normal mounting position.

This is applicable to the LED chip described in the second embodiment aswell.

FIG. 16 shows an example shape of the LED chip in the case where therotative direction at the time of the mounting has judged to beclockwise.

As shown in FIG. 16, in the electrode-opposed region, the electrode edge931 of the n-electrode 93 adjoining the region K, and the electrode edge912 of the n-electrode 91 adjoining the region K′ are formed so as torecede inwardly (draw apart) from the center point (point G) withrespect to the pattern edges 97 and 99 (illustrated in broken line inFIG. 16) of the wiring patterns 96 and 98 (FIG. 8) of the LED chiptaking the normal mounting position. The electrode edge 911 of thep-electrode 91 adjoining the region K and the electrode edge 932 of then-electrode 93 adjoining the region K′ do not recede inwardly, whichmeans that they are at the conventional positions.

In this way, by forming the electrode edges so as to recede inwardly andnot to lap over the wiring patterns even if the LED chip is rotatedclockwise several degrees at the time of the flip chip mounting, itbecomes possible to prevent the p-electrode and the n-electrode fromcausing a short circuit in the case where the LED chip is mounted afterit is rotated clockwise several degrees from its normal mountingposition.

Note that in the case where the rotative direction at the time of themounting is anticlockwise, the electrode edges 911 and 932 recedeinwardly, and 912 and 931 do not recede on the contrary to theabove-described case.

(6) The structure of the lighting unit including the sixty-four LEDchips flip-chip mounted on the wiring board is described above. Thepresent invention is applicable to a lighting apparatus using thelighting unit as the light source.

FIG. 17 is a perspective view showing an example structure of a lightingapparatus 200.

As shown in FIG. 17, the lighting apparatus 200 has a shape of a lightbulb, and includes a case 201, a reflecting shade 202, a base 203, and alighting unit 1 as the light source. The size of the base 203 is thesame as the size of a base used for general light bulbs, such asincandescent lamps (i.e. the bases are in the same standard).

A feeding unit (not illustrated) used for feeding the lighting unit 1 isdisposed in the case 201. The feeding unit includes a publicly knowncircuit that converts the alternating current supplied via the base 203to the direct current for lighting the LED chip, and supplies the directcurrent to the lighting unit 1. The lighting unit 1 to be used as thelight source is in a form of a plate. Therefore, the lighting apparatusitself can be downsized to a considerable degree (especially in itsoverall length) compared to incandescent lamps.

The present invention is also applicable to a table lamp, a flashlightand so on, as the lighting apparatus using the above-described lightingunit 1 as the light source.

(7) Although the wiring board described above is a substrate made ofresin, the present invention is not limited to this. For instance, asilicon substrate may be used. Although gold (Au) is used for the wiringpatterns, other materials, with which the ultrasonic bonding isavailable such as copper (Cu), may be used. Although the 300 μm-squareLED chip is used in the above-described embodiments, the size of the LEDchip is not limited to this as a matter of course. For instance, a 100μm-square to 900 μm-square LED chip or an LED chip of millimeters ordermay be used. Especially, the p-electrode and the n-electrode of the LEDchip can be effectively prevented from causing a short circuit in thecase where 100 μm-square to 900 μm-square LED chip are densely mounted.

Furthermore, the present invention is applicable not only to the wiringboard and the LED chip to which the ultrasonic bonding is applied, butalso the cases where other bonding methods which might cause a rotationof the LED chip at the time of the bonding are used. The presentinvention is applicable not only to the LED chip, but also to an opticalsemiconductor bare chip, such as a semiconductor laser, and a printedwiring board used for mounting the bare chip thereon, and a lightingunit and a lighting apparatus using the bare chip.

INDUSTRIAL APPLICABILITY

The present invention is applicable to an optical semiconductor barechip such as an LED, a printed wiring board used for mounting theoptical semiconductor bare chip thereon, a lighting unit, and a lightingapparatus.

1. A printed wiring board having first and second wiring patterns thatare formed on a mounting surface thereof so as to oppose each otheracross an insulating region, an optical semiconductor bare chip beingflip-chip mounted on the mounting surface and having, on one surfacethereof, first and second electrodes that are disposed so as to opposeeach other, and the first and second wiring patterns respectivelycorresponding in position and shape to the first and second electrodes,wherein in a plan view of the insulating region divided into a firstregion that includes a point nearest to a center point of the opticalsemiconductor bare chip that takes a normal mounting position, andsecond and third regions that sandwich the first region, (i) an outeredge portion of the first wiring pattern which adjoins the secondregion, and an outer edge portion of the second wiring pattern whichadjoins the third region, and/or (ii) an outer edge portion of the firstwiring pattern which adjoins the third region, and an outer edge portionof the second wiring pattern which adjoins the second region, are formedso as to recede inwardly as a distance from the center point increaseswith respect to outer edges of the first and second electrodes of theoptical semiconductor bare chip that takes the normal mounting position.2. The printed wiring board of claim 1, wherein in a case where adistance between the first and second electrodes measured at any pointis substantially constant, the width of the first region issubstantially constant and substantially equal to the distance betweenthe first and the second electrodes.
 3. The printed wiring board ofclaim 1, wherein the first and second wiring patterns are formed on asurface of an insulating plate that is a composite substrate includingan inorganic filler and a resin composite.
 4. A lighting unit in whichan optical semiconductor bare chip is flip-chip mounted on a printedwiring board thereof, wherein the printed wiring board is one of theprinted wiring boards defined in claim
 1. 5. A lighting apparatuscomprising the lighting unit of claim 4 as a light source.
 6. An opticalsemiconductor bare chip having first and second electrodes that aredisposed on one surface thereof so as to oppose each other across aninsulating region, the semiconductor bare chip being flip-chip mountedon a mounting surface of a printed wiring board having first and secondwiring patterns that are formed on the mounting surface so as to opposeeach other, the first and second wiring patterns respectivelycorresponding in position and shape to the first and second electrodes,wherein in a plan view of the insulating region divided into a firstregion that includes a point nearest to a center point of the opticalsemiconductor bare chip, and second and third regions that sandwich thefirst region, (i) an outer edge portion of the first electrode whichadjoins the second region and an outer edge portion of the secondelectrodes which adjoins the third region, and/or (ii) an outer edgeportion of the first electrode which adjoins the third region and anouter edge portion of the second electrode which adjoins the secondregion, are formed so as to recede inwardly as a distance from thecenter point increases with respect to outer edges of the first andsecond wiring patterns that respectively correspond to the first andsecond electrodes of the optical semiconductor bare chip that takes anormal mounting position.
 7. The printed wiring board of claim 6,wherein in a case where a distance between the first and second wiringpatterns measured at any point is substantially constant, the width ofthe first region is substantially constant and substantially equal tothe distance between the first and the second wiring patterns.
 8. Alighting unit in which an optical semiconductor bare chip is flip-chipmounted on a printed wiring board, wherein the optical semiconductorbare chip is one of the optical semiconductor bare chips defined inclaim
 6. 9. A lighting apparatus comprising the lighting unit of claim 8as a light source.
 10. A lighting unit in which an optical semiconductorbare chip is flip-chip mounted on a printed wiring board thereof,wherein the printed wiring board is one of the printed wiring boardsdefined in claim
 2. 11. A lighting unit in which an opticalsemiconductor bare chip is flip-chip mounted on a printed wiring boardthereof, wherein the printed wiring board is one of the printed wiringboards defined in claim
 3. 12. A lighting unit in which an opticalsemiconductor bare chip is flip-chip mounted on a printed wiring board,wherein the optical semiconductor bare chip is one of the opticalsemiconductor bare chips defined in claim 7.